feat: add foreign method binding infrastructure with IO library integration

Implement the `WrenBindForeignMethodFn` callback type and `bindForeignMethodFn` configuration field to allow host applications to resolve foreign method declarations at class definition time. Refactor the IO library to use this new binding mechanism instead of the previous `wrenDefineStaticMethod` approach, adding `foreign` keyword support to the lexer and compiler. Introduce `freeCompiler` helper for cleanup, store module names in `ObjModule`, and update the VM to call the binder when processing `CODE_METHOD_INSTANCE` and `CODE_METHOD_STATIC` opcodes for foreign methods.

src/cli/vm.c

@@ -8,6 +8,7 @@ WrenVM* createVM()
 {
   WrenConfiguration config;
 
+  config.bindForeignMethodFn = NULL;
   config.loadModuleFn = readModule;
 
   // Since we're running in a standalone process, be generous with memory.